I've completed building a Raspberry Pi 3b, 64bit, Sia Host/Wallet/Node that uses four 2.5" laptop drives in a RAID5 configuration for redundancy. I thought RAID would be useful in preventing lost collateral :)
This is a pre-release of the guide because:

**edit: (6th Aug '17)The blockchain has finished its sync, wallet unlocked, hosting settings set, host announced, awaiting contracts. Sync time approx 56 hours from block 0. Post sync currently using 2% CPU and 43% of Pi memory. I consider this guide complete now as in the 3 days this has been public I've not been informed of concerns security related. I'll leave the original section of this post below for context.

The guide will continue to progress. I intend to implement Sia-Cluster next for easier user monitoring.

**end of edit

The Pi is just finishing up syncing the blockchain. Once it has done this I will have access to my funds for hosting and I will consider this project completed. Before that happens I would appreciate a careful set of eyes on the build to confirm whether or not the system is secure. This is the first time I have done a pre-release of a guide, but it is the uniqueness of Sia that it needs the wallet permanently unlocked that makes me want to be absolutely certain.

All feedback welcome, and there are a few other notes/comments at the bottom of the guide concerning an auto-boot feature.

@maol I was aware of it from the reddit post. Just had to look up the username to check. I was previously trying to get Sia to work with another users version of a 64bit Pi OS without success. Ketes post made me aware Gentoo was the way to go.

I think me and Kete (reddit /u/ketetefid) have slightly different approaches to the guides:
He has very helpfully made an image to download for users with minimal Sia or Raspberry Pi knowledge to get Sia running.
Where possible I aim my guides at a project builder. Eg the step by step of how to build from scratch, including hardware, for two reasons.

Security: By downloading the generic OS image and each package as needed from official sources, a user can be fairly confident that nothing has been tampered with or malicious scripts added. Whilst this is not at this time a known used attack vector, I believe it to be good practice for a device with an open wallet and funds. I would not want to be responsible for an image that was tampered with.

Education: Sia and all currencies generally I believe are still in the development phase and the more people build units like this themselves, the more of an understanding people will have of the technology. I'd also like the guide to be in a condition where an intermediate user could tailor their device slightly to their needs. Perhaps they'll think of something we haven't and improve on it for the benefit of the community. For example using the guide and extrapolating, (with a sufficient power supply and USB hubs) if someone wanted to add 127 HDDs to it they could.

And I've added the reddit link to the original post in the first message.

@xadhoom I'm not too familiar with nextcloud or how it would fit in with this device. If you want a Raspberry Pi NAS for backing up and storing files on a home/small business network then I would strongly recommend OpenMediaVault and a device similar in hardware to mine. Then it just sits on the network as a network drive. Again RAID redundancy is available, really simple UI. That would protect you from most things except fire/theft.

Nextcloud seems to be the renter end of the service if my quick glance is correct. Can you host to Nextcloud?

I get there is a desire for as sleek as possible usability.

Once configured, this device in my guide needs little to no maintenance and just occasional monitoring. My next step is to integrate Sia-Cluster for it's sleek browser based monitoring for pricing and storage stats.